Blow molded plastic container and method of making

ABSTRACT

A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, and a bottom portion. The bottom portion includes a central pushup area that is substantially symmetrical about the longitudinal axis and that is substantially flat. The pushup area preferably has a radius that is within the range of 0.100 inches to 0.500 inches. The bottom portion further includes a plurality of support feet surrounding and protruding downwardly from the pushup area, each of which has a bottom support surface and a pair of sidewalls that help define a valley between the support feet. The sidewalls have a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, and this angle is at least 25 degrees.

1. This is a continuation-in-part of Ser. No. 08/551,323, filed Nov. 1, 1995, the disclosure of which is hereby incorporated as if it were fully set forth herein.

BACKGROUND OF THE INVENTION

2. 1. Field of the Invention

3. This invention relates broadly to the field of container making, and more specifically to blow molded plastic bottles, such as the PET bottles that are in common use today for packaging soft drinks such as soda.

4. 2. Description of the Prior Art and More Recent Technology

5. During the last twenty-five years or so, there has been a dramatic shift in the packaging of carbonated beverages, particularly, soft drinks, away from glass containers and toward plastic containers. The plastic containers initially took the form of a two-piece construction, wherein a plastic bottle having a generally hemispherical bottom was applied a separate base cup, which would permit the bottle to be stood upright. The hemispherical bottom was seen as the most desirable shape for retaining the pressure generated by the carbonation within the container. Pressures in such containers can rise to 100 p.s.i. or more when the bottled beverage is exposed to the sun, stored in a warm room, car trunk, or the like.

6. Such plastic containers represented a significant safety advantage over glass containers when exposed to the same internal pressures. However, the two-piece construction was not economical because it required a post molding assembly step, and, also a separation step prior to reclaiming or recycling the resins forming the bottle and base cup.

7. During this period of development, various attempts were made to construct a one-piece, self-supporting container that would be able to retain the carbonated beverages at the pressures involved. Such a one-piece container requires the design of a base structure which will support the bottle in an upright position and will not bulge outwardly at the bottom. A variety of designs were first attempted, with most following one of two principal lines of thought. One line of designs involved a so-called champagne base having a complete annular peripheral ring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726; 3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety of designs is that which included a plurality of feet protruding downward from a curved bottom. Examples of this variety are to be found in U.S. Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323. In recent years, the latter type of design has achieved primacy in the marketplace.

8. Footed one piece bottles present certain problems, though, which have not yet been worked out to the satisfaction of the packaging industry and its customers. For example, the uneven orientation of the polymer in the footed area of the bottom can contribute to uneven post filling expansion of either one or more feet or the central portion of the bottom, creating what is generally referred to as a “rocker.” In addition, the presence of the feet themselves and the need to force the oriented material into the shape of the feet can create stress points in the container bottom that can adversely affect container shape. Container bottom designs that minimize stress and disorientation of the polymer during molding, then are considered preferable.

9. Another concern in the design of container bottoms for one piece containers is the possibility of stress cracking in the base. The amount of stress cracking is related to the geometry of the base. Relatively large radius curves in the base will reduce the stress cracking compared to a base with small radius curves.

10. Yet another factor that is important in the design of such containers is volumetric and structural stability of the container during and after filling and pressurization of the container. Bulging of vulnerable areas in the container bottom, particularly the pushup area in the center, will increase the volume of the container and affect the filling process, as well as permit visible accumulation of gases at the top of the bottle, which will be visible to the consumer. Such deformation is preferably to be avoided.

11. A need exists for an improved bottom design for a polymeric one piece container that will optimize use of material relative to strength, reduce the possibility of stress cracking, reduce deformation during filling and storage, and permit molding with a minimum of stress and disorientation of the polymer material.

SUMMARY OF THE INVENTION

12. Accordingly, it is an object of the invention to provide an improved bottom design for a polymeric one piece container that will optimize use of material relative to strength, reduce the possibility of stress cracking, reduce deformation during filling and storage, and permit molding with a minimum of stress and disorientation of the polymer material.

13. In order to achieve the above and other objects of the invention, a molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall; and a bottom portion including a central pushup area that is substantially symmetrical about the longitudinal axis, said pushup area being substantially flat and having a radius that is within the range of 0.100 inches to 0.500 inches; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface and a pair of sidewalls, each of the sidewalls helping define a valley between said support feet, and wherein at least one of the sidewalls has a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, the angle being at least 25 degrees; and a plurality of ribs positioned in the valleys between the support feet, each of the ribs being positioned between and helping to define two of the support feet.

14. According to a second aspect of the invention, a molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall; and a bottom portion including a plurality of downwardly protruding support feet, each of the support feet having a bottom support surface and a pair of sidewalls, each of the sidewalls helping define a valley between the support feet, and wherein at least one of the sidewalls has a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, the angle being at least 25 degrees, whereby the container bottom is easier to mold than those heretofore known.

15. These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

16.FIG. 1 is a longitudinal cross-section of an improved polymeric container that is constructed according to a preferred embodiment of the invention;

17.FIG. 2 is a close-up view of a bottom portion of what is depicted in FIG. 1;

18.FIG. 3 is a perspective depiction of the bottom of the container that is shown in FIGS. 1 and 2;

19.FIG. 4 is a side elevational depiction of the container bottom that is shown in FIGS. 1-2;

20.FIG. 5 is a bottom plan view of the container bottom that is shown in FIGS. 1-4;

21.FIG. 6 is a longitudinal cross-section of a container that is constructed according to a second embodiment of the invention; and

22.FIG. 7 is a fragmentary sectional view taken through one of the ribs in the embodiment of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

23. Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIGS. 1 and 2, a molded polymeric container 10 that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, includes, according to a preferred embodiment of the invention, a substantially cylindrical body portion 12 that has a longitudinal axis 18 and a circumferential sidewall 13. Sidewall 13 is separated from the longitudinal axis 18 by a so-called label radius R_(L). As is typical in such containers, polymeric container 10 includes a neck portion 14 that tapers into a threaded nipple that defines an opening 16. Container 10 further includes a bottom portion 20 including a central pushup area 30 that is substantially symmetrical about the longitudinal axis 18 of the cylindrical body portion 12 of the molded polymeric container 10. Bottom portion 20 further includes a plurality of support feet 22, of which there are five in the preferred embodiment, that surround and protrude downwardly from the pushup area 30. Each of the support feet 22 has a bottom support surface 24, shown in FIG. 2, that has radially inner edge 26 and a radially outer edge 28, also shown in FIG. 2. The radially inner edges 26 of the respective support feet 22 together circumscribe an inner ring 32, that is visible in FIG. 5 and has a radius R_(P) that surrounds the central pushup area 30. The support feet 22 extend downwardly from a central point of the pushup area 30 by a longitudinal distance D_(P).

24. The bottom portion 20 of the molded polymeric container 10 further includes a plurality of ribs 34, each of which is positioned between and helps to define two of the support feet 22, as may be best seen in FIGS. 3, 4 and 5. Each of the ribs 34 has a radius of curvature R₅, as is shown diagrammatically in FIGS. 1 and 2.

25. As may be seen in FIG. 2, a whole cross section taken longitudinal of the bottom portion 20 of container 10 will reveal that the support foot 22 is preferably formed with a first broad radiused side surface that is curved at a first radius R₁, which merges into a second, tighter radiused outer transition surface that has a curvature radius R₂. The outer transition surface R₂ merges into the flat bottom support surface 24 at the outer edge 28, as may be clearly seen in FIG. 2. At the inner edge 26 of the bottom support surface 24, the support foot 22 yields to a transition area 36 that is positioned between the center point of the pushup area 30 and the inner edge 26 or inner ring 32 of the support foot 22. This transition area is characterized by a central dome that has a lower concave surface that is curved at a radius R₄, and a compensating area with a lower convex surface that curves at a radius R₃, and merges into the bottom of the support feet 22 at the inner edge 26 as shown in FIG. 2. Preferably, R₄ and R₃ should be no less than about 0.900 inches, and R₂ should be no less than about 0.500 inches.

26. According to one important aspect of the invention, the radius R_(P) of the pushup area 30 is between 10% to 50% of the radius R_(L) of the sidewall 13 of the body portion 12, so that the pushup area 30 constitutes a relatively small proportion of the total area of the bottom portion 20. This reduces downward deflection of the pushup area 30 when the container 10 is pressurized with, for example, a carbonated beverage. More preferably, the radius R_(P) of the pushup area 30 is between about 25% to about 47% of the radius R_(L) of the sidewall 13. Most preferably R_(P) is about 45% of the radius R_(L).

27. According to another important aspect of the invention, the longitudinal distance D_(P) between the central point of the pushup area 30 and the bottom of the support feet 22 is no more than 100% of the radius R_(P) of the pushup area 30. As a result of this, the transition area 36 that is defined between the central point and the inner ring 32 is relatively shallow, thus reducing stresses in the transition area 36 during use of the container and strengthening the container. More preferably, the distance D_(P) is between about 15% to about 50% of the radius R_(P), and is most preferably between about 22% to about 28% of the radius R_(P).

28. Another important feature of the invention is that the radius of curvature R₅ of the ribs 34 is no less than about 70% of the radius R_(L) of the sidewall 13 of the body portion 12, so that the bottom portion 20 of the container 10 will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. More preferably, the radius of curvature R₅ of the ribs 34 is no less than about 90% of the radius R_(L) of the sidewall 13, and is most preferably no less than about 99% of the radius R_(L) of the sidewall 13.

29. The longitudinal distance D_(P) between the central point of the pushup area 30 and the bottom of the support feet 22 is preferably no more than about 0.5 inches, and may be as little as 0.15 inches. The radius R_(P) between the longitudinal axis 18 and the inner ring 32 of the container bottom 20 may be as little as about 0.25 inches, and as great as about 1.2 inches. The smaller this dimension, the less deformation or bulging that is likely to occur when the container can is pressurized.

30. Preferably, container 10 is fabricated of PET. Alternatively, it may be fabricated from PEN or a PEN-PET copolymer or physical blend of the two.

31. Container 10 may be molded according to known techniques from a parison in a mold that is contoured according to the dimensions and shape disclosed herein. During such molding, the bottom portion 20 of the container will be kept constrained in a substantially hemispherically shape because of the hemispherically shaped ribs 34 that help define support feet 22. Accordingly, molding will be accomplished with a minimum of disorientation and stress on the polymeric material.

32. A molded polymeric container 42 that is constructed according to a second aspect of the invention is depicted in FIGS. 6 and 7. Container 42 includes a bottom portion 44 having a central pushup area 46 that is substantially symmetrical about the longitudinal axis of the container 42. The pushup area contains a substantially flat central portion 48, which has a radius R_(F) that is within the range of 0.100 inches to 0.500 inches. More preferably the radius R_(F) is about 0.150 inches. The presence of the substantially flat area has been found to increase the burst resistance of the container in the critical area near the center of the bottom portion 44. This area tends to be more susceptible to bursting and stress cracking than other areas of the container bottom, because the PET material in this area tends to be more amorphous and less oriented than at the other areas. The presence of the flat area 48 avoids geometric points of stress concentration, which acts to increase the burst resistance of the container bottom.

33. To avoid creating excessively severe transition angles (corresponding to reference number 36 in FIG. 2), the radius R_(P) of the pushup area 46 is may be increased by a distance that is equal to the radius R_(F) of the flat portion 48.

34. Container 42 includes a plurality of support feet 22 surrounding and protruding downwardly from the pushup area 46. Each of the support feet 46 has a bottom support surface 24 and a pair of sidewalls 51, each of the sidewalls 51 helping define a valley 56 between the support feet 46, as may be seen in FIG. 7. At least one of the sidewalls 51 has a substantially straight portion 52 that defines an angle α with respect to a line 50 that is perpendicular to the longitudinal axis of the container 42. Angle α is at least 25 degrees and most preferably is about 30 degrees. In the first embodiment described above, the corresponding angle was only about 20 degrees. It has been found that by increasing the angle α the moldability of the container increases, which serves to permit more efficient manufacturing and lightweighting of the container.

35. It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, comprising: a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall; and a bottom portion comprising: a central pushup area that is substantially symmetrical about the longitudinal axis, said pushup area being substantially flat and having a radius that is within the range of 0.100 inches to 0.500 inches; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface and a pair of sidewalls, each of said sidewalls helping define a valley between said support feet, and wherein at least one of said sidewalls has a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, said angle being at least 25 degrees; and a plurality of ribs positioned in said valleys between said support feet, each of the ribs being positioned between and helping to define two of the support feet.
 2. A container according to claim 1 , wherein said pushup area has a radius that is approximately 0.150 inches.
 3. A container according to claim 1 , wherein said angle is approximately 30 degrees.
 4. A container according to claim 3 , wherein each of said sidewalls contains a substantially straight portion.
 5. A container according to claim 1 , wherein each of said sidewalls contains a substantially straight portion.
 6. A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, comprising: a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall; and a bottom portion comprising: a plurality of downwardly protruding support feet, each of the support feet having a bottom support surface and a pair of sidewalls, each of said sidewalls helping define a valley between said support feet, and wherein at least one of said sidewalls has a substantially straight portion that defines an angle with respect to a line that is perpendicular to the longitudinal axis, said angle being at least 25 degrees, whereby the container bottom is easier to mold than those heretofore known.
 7. A container according to claim 6 , wherein said angle is approximately 30 degrees.
 8. A container according to claim 8 , wherein each of said sidewalls contains a substantially straight portion. 